Heat exchanger



Jime17,1969 I NB-RUNNER 3,450,198

HEAT EXCHANGER.

Filed March a, 1966 Sheet of 2 ALFRED BRUNNER W ZATTO EVS A. BRUNNERHEAT EXCHANGER June 17, 1969 Sheet 3 of2 Filed March 8, 1966 Inventor:AL FRED BRUNNEF? AT'T'QR EYS "United States Patent 3,450,198 HEATEXCHANGER Alfred Brunner, Winterthur, Switzerland, assignor to SulzerBrothers, Limited, Winterthur, Switzerland, a corporation of SwitzerlandFiled Mar. 8, 1966, Ser. No. 532,721 Claims priority, applicationSwitzerland, Mar. 12, 1965,

3,499 Int. Cl. F28f 27/02 U.S. Cl. 165-101 9 Claims ABSTRACT OF THEDISCLOSURE This invention relates to a heat exchanger. Moreparticularly, this invention relates to a heat exchanger for a nuclearreactor. Still more particularly, this invention relates to a heatexchanger of composite structure which provides a uniform pressurepattern to a medium flowing therethrough.

Heretofore, the heat exchangers of composite structure have been used innuclear reactors for absorbing the heat carried by the reactor coolant.These heat exchangers have been comprised of a plurality of parallelconnected heat exchange units having a heat absorbing medium flowingtherein and have been arranged in a casing so that the reactor coolantflows directly through the heat exchanger casing over the heat exchangeunits.

Since the coolant usually undergoes a considerable pressure drop inpassing through the heat exchanger, considerations of heat expansionmake it essential for the units to be disposed in the heat exchanger inspaced relation. As a consequence, the lateral boundary walls of theunits have had to be strengthened.

In order to provide a solution to the problem created by pressure drops,it has been suggested that the heat exchanger units which may be of anypolygonal shape be erected in a plurality of open-ended containershaving closed walls for disposition on stilts, a support lattice or agrating so that the containers are arranged alongside each other in situwith the gaps between each pair of adjacent containers bridged bysealing means at top and bottom. However, when a considerable pressuredrop occurs along the coolant flow path through these heat exchangers, apositive pressure acts on the container side walls at the sealed endswhich is either internal or external to the walls depending on the endof the container involved. Thus, the lateral walls must be strengthened.This requires not only extra material but also extra space since thewalls have generally been made of corrugated plates.

Accordingly, it is an object of this invention to provide a heatexchanger having a plurality of spaced heat exchanger units wherein thepressure patterns in the spaces between the units is substantially thesame as the pressure patterns within the units.

It is another object of this invention to provide a heat exchangerhaving a plurality of spaced heat exchanger units with throttling meansin the spaces between the units.

It is another object of this invention to provide a heat exchangerhaving a plurality of spaced heat exchanger units with vertically spacedthrottling plates in the spaces between the units.

It is another object of this invention to provide a plurality of spacedheat exchanger units of a heat exchanger with perforated walls incommunication with each other.

Generally, this invention provides a heat exchanger comprising aplurality of open-ended spaced heat exchanger units for absorbing heatfrom a flow of coolant passingtherethrough with a throttling meansdisposed in the spaces between adjacent heat exchanger units forthrottling the flow of coolant through the spaces. The throttling meansincludes a plurality of movably mounted spaced throttling elements whichare supported on the wall of one heat exchanger unit and which bearagainst the wall of an adjacent heat exchanger unit at different levels.

The invention avoids any unbalanced pressure loading on the exteriorwalls of the units by substantially equalizing the pressures on oppositesides of the exterior walls. Further, the invention allows adjacent heatexchanger units, assuming they are of square shape, to have two oppositewalls formed of i mperforate plates or sheets while the other two wallsare formed of spaced apart plate strips so as to form perforated walls.In such a modification there is a direct pressure equalization betweenthe interior of the units and the spaces between adjacent units.

Additionally, in the latter case, the invention provides sometemperature equalization between the coolant flowing through the spacesbetween adjacent units and the coolant flowing in the units. The degreeof temperature equalization can be improved by staggering the aperturesin the exterior walls of adjacent units relative to each other betweenadjacent throttling elements so that a flow of coolant can betransversely directed from between the units into the units. Thetransverse flow, however, is substantially smaller than the flow ofcoolant in the units.

According to a further modification of the invention, the heat exchangerunits are vertically disposed to each other and each is provided withtu-be bunches for the flow of heat absorbing medium therethrough whichare disposed in a scaffold-like structure having longitudinal andtransverse struts. The transverse struts of adjacent uni-ts areinterconnected in a number of stages or tiers by the throttling elementsand the longitudinal struts are aligned in parallel relation to thedirection of flow of coolant over the tubes.

In like manner, the outside units of the heat exchanger are sealed orthrottled with respect to the walls of the casing in which the heatexchanger is mounted.

The throttling elements comprise a sheet metal strip which is mounted onthe wall of one unit at a level below the point of contact with theadjacent unit. However, the throttling elements can be formed of barmaterial of U- or T-shaped sections.

These and other objects and advantages will become more apparent fromthe following detailed description taken in conjunction with theaccompanying drawings in which:

FIG. 1 illustrates a cross-sectional view of a nuclear reactor having aheat exchanger of the invention disposed therein;

FIG. 2 illustrates a partial cross-sectional view of a pan of adjacentheat exchange units of the heat exchanger of FIG. 1;

FIG. 3 illustrates an enlarged cross-sectional view of a throttlingmeans between the heat exchanger units of FIG. 2; and

FIG. 4 illustrates a modification of the invention.

Referring to FIG. 1, a nuclear reactor in which the invention can beutilized includes a reactor core R which is received in apressure-resistant structure, for instance, of concrete. A large numberof heat exchange units E are disposed below the core R in a passage Kwhich in this particular case forms the casing of the heat exchangeraccording to the invention and cover plates A are provided to seal thespace between the elements and the heat exchanger casing wall. In thisparticular embodiment, those boundary walls of the units which areadjacent the casing wall take the form of strengthened sheetmetal wallswhile the spaces S between the units are interconnected in stages bythrottling elements in the manner clearly apparent from FIG. 2, whichwill be described hereinafter.

A reactor coolant, e.g. CO flows downwards through the reactor core andpasses therefrom to the heat exchanger which is formed by the units E toheat a mediume.g., water, flowing through the units E. In passingthrough the units E, the coolant is throttled by the tiered throttlingelements in the spaces S between the units E. The coolant then passesfrom the heat exchanger through circulating lines L associated withcirculating blowers U upwardly to re-enter the reactor core.

Referring to FIG. 2, the heat exchanger units 1, 2 of the heat exchangerof FIG. 1, which, for example, are of square cross-section in plan, areopen at top and bottom for the flow of reactor coolant therethrough inthe direction indicated by arrows M. The tubes 3 through which the heatabsorbing medium flows are arranged in bunches of parallel flat-typetube coils so that the coolant flows transversely over the tubes. Inorder to illustrate the invention with clarity, FIG. 2 shows the tubes 3disposed in only one of the heat exchanger units but it is to be notedthat all the units have similar tubes mounted therein during use.Further, in order to more clearly describe the environment of theinvention, the heat exchanger is of a size which measures 2 m. x 2.5 m.x 10 m. and weighs about 100 tons.

The straight parallel portions of the tubes 3 are formed with circularribs 4 and interconnected by unribbed reversing bends 5 to form flatparallel tube panels through which the heat absorbing medium flows. Theunits enclose the tube panels with a scaffold-like structure comprisinglongitudinal and transverse struts or the like, in the form of fourbearing longitudinal struts 6 to which transverse struts 7, 8, embodiedas T bearers, are welded in a number of tiers with angle-member bearers9, 10 forming a top frame and bottom frame respectively. The tube panelsare secured by flanges 11 to the webs 12 of the transverse struts 7,such webs forming support or bearing edges 12. The webs 12 are in turnwelded to the arms of the longitudinal struts 6 which are contiguous onthe opposite sides. Conveniently, the webs 12 are disposed in staggeredrelationship to one another on the two opposite sides of each unit.

When the units are assembled, the tube panels are placed in a planeparallel to the plane of the drawing, then introduced between thetransverse struts which have the edges 12, and secured by means of theflanges 11 thereto. Only after all the tube panels are secured is thefront frame welded on. In the drawing, the visible transverse struts ofthe rear frames of the units are indicated by reference character 8.

According to the invention, the transverse struts of adjacent units areinterconnected at least in a number of stages by throttling elements. Inthe embodiment shown in FIG. 2, the space 13 between the units 1 and 2is bridged in a number of tiers by throttling elements 14, so that theflow of gas around the pipes is severely throttled in the spaces 13.Since the gas flow is intensively throttled not only by the elements 14in the spaces 13 between adjacent units but also by the edges 12 nearthe unribbed tube bends, most of the gas flow is confined to the regionof the ribbed straight tube portions 3. Consequently, the temperaturedistribution of the gas at the end of the heat exchanger is uniform overthe whole crosssection. Also, there is pressure equalization in thesections between the various units and between the spaces which existbetween adjacent units so that there is no unequal stressing of theinsides or outsides of the various units.

As above stated, there is also some temperature equalization between themedium flowing around the tubes and the medium flowing through thespaces. Advantageously, to further improve this temperature equalizer,the units can be specially devised to produce, as compared with thelengthwise flow of the heat absorbing medium through the units, areduced transverse flow between the units and the spaces. One way ofproducing such a transverse flow is for the transverse struts ofadjacent units to be vertically staggered relatively to one another.Alternatively, inclined baffles can be provided near the tube bendsbetween two transverse struts of the same unit, or else the entrycross-section of that proportion of the medium of one unit which flowsthrough the units can be reduced relatively to the entry cross-sectionof the other, for instance, by appropriately devising the top frame ofthe angle-member bearers 9, and the outflow cross-section of anotherunit separated from the first-mentioned unit by a number of units can bereduced similarly in relation to the other outflow cross-sections bysimilarly devising the angle-member bearers 10 which form the bottomframe.

As above stated, there is noneed for the throttling elements tocompletely seal off the various space sections from one another; allthat is needed is for the flow in the spaces to be intensivelythrottled. The lengthwise gas flow through the spaces which are e.g. 5cm, wide, is small as compared with the gas flow through the units;also, the lengthwise gas flow through the spaces is mixed in the varioussections with cooled gas from the units so that the gas flow from thespaces has substantially the same temperature as the gas flow in theunits. Consequently, there is substantially uniform thermal stressing ofthe constructional elements.

Referring to FIGS. 2 and 3, the transverse struts 7 as well as thetransverse struts S of adjacent units are interconnected by throttlingelements 14 which are disposed in all tiers of adjacent units to bebridged; however, arrangements are of course possible wherein only someof the transverse struts of adjacent units are interconnected bythrottling elements.

The throttling elements 14 take the form of sheetmetal strips which areborne by continuous projections or troughs 15 contrived on thetransverse struts 7 of one unit. The strips 14 are wider, preferablyabout 1.4 times wider, than the longest space 13 between any twoadjacent units and extend at an inclination over the space against thecorresponding transverse strut 7 of the adjacent unit under a slightpositive gas pressure of the coolant. The chain-dotted lines in FIG. 3indicate how the strips 14 are secured to the strut 7 by means ofnumbered retaining stirrups 16, before and after the various units areslid together. Once the units have been slid together, the stirrups 16are removed allowing the throttling strips 14 to automatically take upthe inclined position shown. It the stirrups 16 are numbered, acontinuous check can be made during assembly to see that all the strips14 have definitely been released by the stirrups 1-6.

The sealing lines of the strips 14 extend horizontally between thestrips 14 and the two adjacent struts 7; however, arrangements are ofcourse possible wherein the sealing lines extend at an inclination tothe vertical. This feature depends mainly upon how the various units aredisposed and constructed.

Referring to FIG. 2, the space 13 is sealed at the top by a T-bar 17 andthe pressure of the gaseous heat vehicle on the angle-member bearers 9of two adjacent units. The web of the T-bar 17 in the space centers thebar while the bar flanges bridge the space.

Instead of using flattened strips 14, the transverse struts 7 ofadjacent units can be interconnected in stages by U-bars 18 over thespace as shown by example in chain-dotted lines in FIG. 2. In thisparticular embodi' ment, the units are erected on a support gratingwhich is formed from box girders; one such grating 19 being shown inFIG. 2. The heat exchanger is so devised in accordance with theinvention that the bearing box girders need not be specially sealed 01ffrom the units at the bottom of the heat exchanger.

The outer units of the heat exchanger can have, for instance, on theiroutsides, a strengthened continuous wall (FIG. 1). Preferably, however,the spaces between the outsides of the outer elements and the heatexchanger casing wall is bridged in tiers or stages by sealing elements,similarly to the tiered or stagewise sealing of the spaces between thevarious units.

Referring to FIG. 4, edges 21 are disposed in tiers or stages or storieson the cylindrical casing wall 20 of the heat exchanger for cooperationwith the throttling elements 14 of the adjacent units. Disposed at thetop is a T-bar 22 Whose web engages with a centering action in the spacebetween the casing wall and the outer units, while the flanges of thebar bear the one on the top edge 21 of the casing wall and the other onthe top bearers 9 of the outer units.

The term throttling element is not to be understood in the presentcontext in the sense of an element eifecting a tight sealing effect;rather, the term is intended to indicate an element which serves tothrottle the flow of the medium through the spaces so that the pressurepattern of the medium flowing through the spaces is substantiallyadapted to the pressure pattern of the medium flowing around the flowpassages in the units. This effectively prevents the formation ofshort-circuit flows along the spaces which short-circuit flows wouldcause thermodynamic losses impairing eflicient heat exchange and alsolead to heavy thermal stressing of the materials used for theconstructional elements.

Having thus described the invention it is not intended that it be solimited as changes may be readily made therein without departing fromthe scope of the invention. Accordingly, it is intended that the subjectmatter described above and shown in the drawings be taken asillustrative and not in a limiting sense.

What is claimed is:

1. A heat exchanger comprising a plurality of openended heat exchangerunits for absorbing heat from a flow of heated coolant passingtherethrough, each pair of adjacent heat exchanger units being sealinglyconnected to each other at the end thereof and being disposed in afreely expandible manner to each other at the opposite end thereof todefine a gap therebetween, and throttling means movably mounted acrosssaid gap between each said pair of adjacent heat exchanger units forthrottling a flow of heated coolant passing through said gap whereby thepressure pattern of the flow of heated coolant passing through each saidgap substantially corresponds to the pressure pattern of the flow ofheated coolant passing through said heat exchanger units defining saidgap.

2. A heat exchanger as set forth in claim 1 wherein 6 said throttlingmeans includes a plurality of vertically spaced throttling elementslongitudinally of each said gap.

3. A heat exchanger as set forth in claim 2 wherein said throttlingelements comprise a flattened strip supported at one elevation on one ofsaid heat exchanger units and bearing against an adjacent heat exchangerunit at a second elevation.

4. A heat exchanger as set forth in claim 3 wherein said secondelevation is disposed above said first elevation.

5. A heat exchanger as set forth in claim 1 wherein each of said heatexchanger units has at least one perforated wall adjacent a perforatedwall of an adjacent heat exchanger unit, said throttlingmeansinterconnecting the imperforated areas of said adjacent perforated wallsin vertical spaced tiers.

6. A heat exchange as set forth in claim 1 wherein the throttled flow ofcoolant between said adjacent heat exchanger units is directedtransversely into the flow of coolant passing through said heatexchanger units.

7. A heat exchanger as set forth in claim 6 wherein said transverse flowof coolant is substantially smaller than said flow of coolant passingthrough said heat exchanger units.

8. A heat exchanger as set forth in claim 1 wherein each of said heatexchanger units includes a scaifold-like structure comprisinglongitudinal struts and T-shaped transverse struts connected togetherand a plurality of tube panels for conveying a heat absorbing mediumtherethrough enclosed within said scaffold-like structure, each saidtube panel being secured to the web of one of said transverse struts,said throttling means interconnecting said transverse struts of eachpair of adjacent heat exchanger units.

9. In combination, a plurality of spaced apart openended heat exchangerunits for absorbing heat from a flow of heated coolant passingtherethrough, and throttling elements movably mounted across the spacesbetween adjacent heat exchanger units for throttling a flow of heatedcoolant passing therethrough whereby the pressure pattern of the flow ofheated coolant passing between said heat exchanger units substantiallycorresponds to the pressure pattern of the flow of heated coolantpassing through said heat exchanger units.

References Cited UNITED STATES PATENTS 1,571,575 2/1926 Darrah 26320FOREIGN PATENTS 667,720 6/ 1929 France.

ROBERT A. OLEARY, Primary Examiner. THEOPHIL W. STREULE, AssistantExaminer.

U.S. Cl. X.R. 26320

